Stimulation of cannabinoid receptor 2 (CB2) suppresses microglial activation

G protein-coupled receptors as therapeutic targets for multiple sclerosis

G protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants. They are considered as the most successful therapeutic targets for a broad spectrum of diseases. Multiple sclerosis (MS) is an inflammatory disease that is characterized by immune-mediated demyelination and degeneration of the central nervous system (CNS). It is the leading cause of non-traumatic disability in young adults. Great progress has been made over the past few decades in understanding the pathogenesis of MS. Numerous data from animal and clinical studies indicate that many GPCRs are critically involved in various aspects of MS pathogenesis, including antigen presentation, cytokine production, T-cell differentiation, T-cell proliferation, T-cell invasion, etc. In this review, we summarize the recent findings regarding the expression or functional changes of GPCRs in MS patients or animal models, and the influences of GPCRs on disease severity upon genetic or pharmacological manipulations. Hopefully some of these findings will lead to the development of novel therapies for MS in the near future.

Decreased cocaine motor sensitization and self-administration in mice overexpressing cannabinoid CB₂ receptors

The potential involvement of the cannabinoid CB₂ receptors (CB₂r) in the adaptive responses induced by cocaine was studied in transgenic mice overexpressing the CB₂r (CB₂xP) and in wild-type (WT) littermates. For this purpose, the acute and sensitized locomotor responses to cocaine, conditioned place preference, and cocaine intravenous self-administration were evaluated. In addition, we assessed whether CB₂r were localized in neurons and/or astrocytes, and whether they colocalized with dopamine D1 and D2 receptors (D1Dr and D2Dr). Dopamine (DA) extracellular levels in the nucleus accumbens (NAcc), and gene expression of tyrosine hydroxylase (TH) and DA transporter (DAT) in the ventral tegmental area (VTA), and μ-opioid and cannabinoid CB₁ receptors in the NAcc were also studied in both genotypes. CB₂xP mice showed decreased motor response to acute administration of cocaine (10-20 mg/kg) and cocaine-induced motor sensitization compared with WT mice. CB₂xP mice presented cocaine-induced conditioned place aversion and self-administered less cocaine than WT mice. CB₂r were found in neurons and astrocytes and colocalized with D2Dr in the VTA and NAcc. No significant differences in extracellular DA levels in the NAcc were observed between genotypes after cocaine administration. Under baseline conditions, TH and DAT gene expression was higher and μ-opioid receptor gene expression was lower in CB₂xP than in WT mice. However, both genotypes showed similar changes in TH and μ-opioid receptor gene expression after cocaine challenge independently of the pretreatment received. Importantly, the cocaine challenge decreased DAT gene expression to a lesser extent in cocaine-pretreated CB₂xP than in cocaine-pretreated WT mice. These results revealed that CB₂r are involved in cocaine motor responses and cocaine self-administration, suggesting that this receptor could represent a promising target to develop novel treatments for cocaine addiction.

The fatty acid amide hydrolase inhibitor URB597 exerts anti-inflammatory effects in hippocampus of aged rats and restores an age-related deficit in long-term potentiation

BACKGROUND

Several factors contribute to the deterioration in synaptic plasticity which accompanies age and one of these is neuroinflammation. This is characterized by increased microglial activation associated with increased production of proinflammatory cytokines like interleukin-1β (IL-1β). In aged rats these neuroinflammatory changes are associated with a decreased ability of animals to sustain long-term potentiation (LTP) in the dentate gyrus. Importantly, treatment of aged rats with agents which possess anti-inflammatory properties to decrease microglial activation, improves LTP. It is known that endocannabinoids, such as anandamide (AEA), have anti-inflammatory properties and therefore have the potential to decrease the age-related microglial activation. However, endocannabinoids are extremely labile and are hydrolyzed quickly after production. Here we investigated the possibility that inhibiting the degradation of endocannabinoids with the fatty acid amide hydrolase (FAAH) inhibitor, URB597, could ameliorate age-related increases in microglial activation and the associated decrease in LTP.

METHODS

Young and aged rats received subcutaneous injections of the FAAH inhibitor URB597 every second day and controls which received subcutaneous injections of 30% DMSO-saline every second day for 28 days. Long-term potentiation was recorded on day 28 and the animals were sacrificed. Brain tissue was analyzed for markers of microglial activation by PCR and for levels of endocannabinoids by liquid chromatography coupled to tandem mass spectrometry.

RESULTS

The data indicate that expression of markers of microglial activation, MHCII, and CD68 mRNA, were increased in the hippocampus of aged, compared with young, rats and that these changes were associated with increased expression of the proinflammatory cytokines interleukin (IL)-1β and tumor necrosis factor-α (TNFα) which were attenuated by treatment with URB597. Coupled with these changes, we observed an age-related decrease in LTP in the dentate gyrus which was partially restored in URB597-treated aged rats. The data suggest that enhancement of levels of endocannabinoids in the brain by URB597 has beneficial effects on synaptic function, perhaps by modulating microglial activation.

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.

The therapeutic potential of the endocannabinoid system for Alzheimer's disease

INTRODUCTION

Dementia currently affects over 35 million people worldwide. The most common form of dementia is Alzheimer's disease (AD). Currently, treatments for AD do not stop or reverse the progression of the disease and they are accompanied by side effects.

AREAS COVERED

The main features of AD pathology, treatment options currently available, the endocannabinoid system and its functionality in general and its role in AD pathology in detail will be outlined. A particular focus will be on the therapeutic potential of the phytocannabinoid cannabidiol.

EXPERT OPINION

Based on the complex pathology of AD, a preventative, multimodal drug approach targeting a combination of pathological AD symptoms appears ideal. Importantly, cannabinoids show anti-inflammatory, neuroprotective and antioxidant properties and have immunosuppressive effects. Thus, the cannabinoid system should be a prime target for AD therapy. The cannabinoid receptor 2 appears to be a promising candidate but its role in AD has to be investigated cautiously. Furthermore, the phytocannabinoid cannabidiol is of particular interest as it lacks the psychoactive and cognition-impairing properties of other cannabinoids. In conclusion, future research should focus on the evaluation of the effects of manipulations to the endocannabinoid system in established animal models for AD, combined with early-phase studies in humans.

Prevention of paclitaxel-induced neuropathy through activation of the central cannabinoid type 2 receptor system

BACKGROUND

Peripheral neuropathy is a major dose-limiting toxicity of chemotherapy, especially after multiple courses of paclitaxel. The development of paclitaxel-induced neuropathy is associated with the activation of microglia followed by the activation and proliferation of astrocytes, and the expression and release of proinflammatory cytokines in the spinal dorsal horn. Cannabinoid type 2 (CB(2)) receptors are expressed in the microglia in neurodegenerative disease models.

METHODS

To explore the potential of CB(2) agonists for preventing paclitaxel-induced neuropathy, we designed and synthesized a novel CB(2)-selective agonist, namely, MDA7. The effect of MDA7 in preventing paclitaxel-induced allodynia was assessed in rats and in CB(2)(+/+) and CB(2)(-/-) mice. We hypothesized that the CB(2) receptor functions in a negative-feedback loop and that early MDA7 administration can blunt the neuroinflammatory response to paclitaxel and prevent mechanical allodynia through interference with specific signaling pathways.

RESULTS

We found that MDA7 prevents paclitaxel-induced mechanical allodynia in rats and mice in a dose- and time-dependent manner without compromising paclitaxel's antineoplastic effect. MDA7's neuroprotective effect was absent in CB(2)(-/-) mice and was blocked by CB(2) antagonists, suggesting that MDA7's action directly involves CB(2) receptor activation. MDA7 treatment was found to interfere with early events in the paclitaxel-induced neuroinflammatory response as evidenced by relatively reduced toll-like receptor and CB(2) expression in the lumbar spinal cord, reduced levels of extracellular signal-regulated kinase 1/2 activity, reduced numbers of activated microglia and astrocytes, and reduced secretion of proinflammatory mediators in vivo and in in vitro models.

CONCLUSIONS

Our findings suggest an innovative therapeutic approach to prevent chemotherapy-induced neuropathy and may permit more aggressive use of active chemotherapeutic regimens with reduced long-term sequelae.

Immunofluorescent spectral analysis reveals the intrathecal cannabinoid agonist, AM1241, produces spinal anti-inflammatory cytokine responses in neuropathic rats exhibiting relief from allodynia

During pathological pain, the actions of the endocannabinoid system, including the cannabinoid 2 receptor (CB(2)R), leads to effective anti-allodynia and modifies a variety of spinal microglial and astrocyte responses. Here, following spinal administration of the CB(2)R compound, AM1241, we examined immunoreactive alterations in markers for activated p38 mitogen-activated protein kinase, interleukin-1β (IL-1β), the anti-inflammatory cytokine, interleukin-10 (IL-10) as well as degradative endocannabinoid enzymes, and markers for altered glial responses in neuropathic rats. In these studies, the dorsal horn of the spinal cord and dorsal root ganglia were examined. AM1241 produced profound anti-allodynia with corresponding immunoreactive levels of p38 mitogen-activated kinase, IL-1β, IL-10, the endocannabinoid enzyme monoacylglycerol lipase, and astrocyte activation markers that were similar to nonneuropathic controls. In contrast, spinal AM1241 did not suppress the increased microglial responses observed in neuropathic rats. The differences in fluorescent markers were determined within discrete anatomical regions by applying spectral analysis methods, which virtually eliminated nonspecific signal during the quantification of specific immunofluorescent intensity. These data reveal expression profiles that support the actions of intrathecal AM1241 control pathological pain through anti-inflammatory mechanisms by modulating critical glial factors, and additionally decrease expression levels of endocannabinoid degradative enzymes.

Bone marrow transplantation confers modest benefits in mouse models of Huntington's disease

Huntington's disease (HD) is caused by an expanded polyglutamine tract in the protein huntingtin (htt). Although HD has historically been viewed as a brain-specific disease, htt is expressed ubiquitously, and recent studies indicate that mutant htt might cause changes to the immune system that could contribute to pathogenesis. Monocytes from HD patients and mouse models are hyperactive in response to stimulation, and increased levels of inflammatory cytokines and chemokines are found in pre-manifest patients that correlate with pathogenesis. In this study, wild-type (WT) bone marrow cells were transplanted into two lethally irradiated transgenic mouse models of HD that ubiquitously express full-length htt (YAC128 and BACHD mice). Bone marrow transplantation partially attenuated hypokinetic and motor deficits in HD mice. Increased levels of synapses in the cortex were found in HD mice that received bone marrow transplants. Importantly, serum levels of interleukin-6, interleukin-10, CXC chemokine ligand 1, and interferon-γ were significantly higher in HD than WT mice but were normalized in mice that received a bone marrow transplant. These results suggest that immune cell dysfunction might be an important modifier of pathogenesis in HD.

Repeated morphine treatment-mediated hyperalgesia, allodynia and spinal glial activation are blocked by co-administration of a selective cannabinoid receptor type-2 agonist

Spinal glial activation has been implicated in sustained morphine-mediated paradoxical pain sensitization. Since activation of glial CB2 cannabinoid receptors attenuates spinal glial activation in neuropathies, we hypothesized that CB2 agonists may also attenuate sustained morphine-mediated spinal glial activation and pain sensitization. Our data indicate that co-administration of a CB2-selective agonist (AM 1241) attenuates morphine (intraperitoneal; twice daily; 6 days)-mediated thermal hyperalgesia and tactile allodynia in rats. A CB2 (AM 630) but not a CB1 (AM 251) antagonist mitigated this effect. AM 1241 co-treatment also attenuated spinal astrocyte and microglial marker and pro-inflammatory mediator (IL-1β, TNFα) immunoreactivities in morphine-treated rats, suggesting that CB2 agonists may be useful to prevent the neuroinflammatory consequences of sustained morphine treatment.

Endocannabinoids and traumatic brain injury

Traumatic brain injury (TBI) represents the leading cause of death in young individuals. It triggers the accumulation of harmful mediators, leading to secondary damage, yet protective mechanisms are also set in motion. The endocannabinoid (eCB) system consists of ligands, such as anandamide and 2-arachidonoyl-glycerol (2-AG), receptors (e.g. CB1, CB2), transporters and enzymes, which are responsible for the 'on-demand' synthesis and degradation of these lipid mediators. There is a large body of evidence showing that eCB are markedly increased in response to pathogenic events. This fact, as well as numerous studies on experimental models of brain toxicity, neuroinflammation and trauma supports the notion that the eCB are part of the brain's compensatory or repair mechanisms. These are mediated via CB receptors signalling pathways that are linked to neuronal survival and repair. The levels of 2-AG, the most highly abundant eCB, are significantly elevated after TBI and when administered to TBI mice, 2-AG decreases brain oedema, inflammation and infarct volume and improves clinical recovery. The role of CB1 in mediating these effects was demonstrated using selective antagonists or CB1 knockout mice. CB2 were shown in other models of brain insults to reduce white blood cell rolling and adhesion, to reduce infarct size and to improve motor function. This review is focused on the role the eCB system plays as a self-neuroprotective mechanism and its potential as a basis for the development of novel therapeutic modality for the treatment of CNS pathologies with special emphasis on TBI.

Prolonged oral cannabinoid administration prevents neuroinflammation, lowers β-amyloid levels and improves cognitive performance in Tg APP 2576 mice

Background

Alzheimer's disease (AD) brain shows an ongoing inflammatory condition and non-steroidal anti-inflammatories diminish the risk of suffering the neurologic disease. Cannabinoids are neuroprotective and anti-inflammatory agents with therapeutic potential.

Methods

We have studied the effects of prolonged oral administration of transgenic amyloid precursor protein (APP) mice with two pharmacologically different cannabinoids (WIN 55,212-2 and JWH-133, 0.2 mg/kg/day in the drinking water during 4 months) on inflammatory and cognitive parameters, and on ¹⁸F-fluoro-deoxyglucose (¹⁸FDG) uptake by positron emission tomography (PET).

Results

Novel object recognition was significantly reduced in 11 month old Tg APP mice and 4 month administration of JWH was able to normalize this cognitive deficit, although WIN was ineffective. Wild type mice cognitive performance was unaltered by cannabinoid administration. Tg APP mice showed decreased ¹⁸FDG uptake in hippocampus and cortical regions, which was counteracted by oral JWH treatment. Hippocampal GFAP immunoreactivity and cortical protein expression was unaffected by genotype or treatment. In contrast, the density of Iba1 positive microglia was increased in Tg APP mice, and normalized following JWH chronic treatment. Both cannabinoids were effective at reducing the enhancement of COX-2 protein levels and TNF-α mRNA expression found in the AD model. Increased cortical β-amyloid (Aβ) levels were significantly reduced in the mouse model by both cannabinoids. Noteworthy both cannabinoids enhanced Aβ transport across choroid plexus cells in vitro.

Conclusions

In summary we have shown that chronically administered cannabinoid showed marked beneficial effects concomitant with inflammation reduction and increased Aβ clearance.

CB2 cannabinoid receptors promote neural progenitor cell proliferation via mTORC1 signaling

The endocannabinoid system is known to regulate neural progenitor (NP) cell proliferation and neurogenesis. In particular, CB(2) cannabinoid receptors have been shown to promote NP proliferation. As CB(2) receptors are not expressed in differentiated neurons, CB(2)-selective agonists are promising candidates to manipulate NP proliferation and indirectly neurogenesis by overcoming the undesired psychoactive effects of neuronal CB(1) cannabinoid receptor activation. Here, by using NP cells, brain organotypic cultures, and in vivo animal models, we investigated the signal transduction mechanism involved in CB(2) receptor-induced NP cell proliferation and neurogenesis. Exposure of hippocampal HiB5 NP cells to the CB(2) receptor-selective agonist HU-308 led to the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin complex 1 (mTORC1) pathway, which, by inhibiting its downstream target p27Kip1, induced NP proliferation. Experiments conducted with the CB(2) receptor-selective antagonist SR144528, inhibitors of the PI3K/Akt/mTORC1 axis, and CB(2) receptor transient-transfection vector further supported that CB(2) receptors control NP cell proliferation via activation of mTORC1 signaling. Likewise, CB(2) receptor engagement induced cell proliferation in an mTORC1-dependent manner both in embryonic cortical slices and in adult hippocampal NPs. Thus, HU-308 increased ribosomal protein S6 phosphorylation and 5-bromo-2'-deoxyuridine incorporation in wild-type but not CB(2) receptor-deficient NPs of the mouse subgranular zone. Moreover, adult hippocampal NP proliferation induced by HU-308 and excitotoxicity was blocked by the mTORC1 inhibitor rapamycin. Altogether, these findings provide a mechanism of action and a rationale for the use of nonpsychotomimetic CB(2) receptor-selective ligands as a novel strategy for the control of NP cell proliferation and neurogenesis.

Targeting CB(2) receptor as a neuroinflammatory modulator in experimental autoimmune encephalomyelitis

During immune mediated demyelinating lesions, the endocannabinoid system is involved in the pathogenesis of both neuroinflammation and neurodegeneration through different mechanisms. Here, we explored the cellular distribution of cannabinoid 2 receptor (CB(2)R) in the central nervous system (CNS) and detected the level of CB(2)R expression during experimental autoimmune encephalomyelitis (EAE) by RT-PCR, Western blot and immunostaining. Our results show that CB(2)R was expressed in neurons, microglia and astrocytes. During EAE, the expression of CB(2)R in spinal cord rose slowly at days 9 and 17 post immunization (p.i.), and elevated rapidly at day 28 p.i., while the expression of CB(2)R in spleen elevated rapidly and got a plateau at days 17 and 28 p.i. Only the increase of CB(2)R expression in spinal cord demonstrated a significant difference when compared to control mice immunized with complete Freund's adjuvant (CFA). The selective CB(2)R antagonist (SR144528) exacerbated EAE clinical severity accompanied by weight loss. SR144528 inhibited the expression of CB(2)R, but increased the expression of CB(1)R in brain, spinal cord and spleen. The administration of SR144528 declined interferon-γ, IL-17, IL-4, IL-10, IL-1β, IL-6 and tumor necrosis factor-α, but increased CX3CL1 in brain and/or spinal cord. In contrast, IL-17 and MCP-1 were increased, while CX3CL1 was decreased in splenic mononuclear cells as compared to vehicle controls. These results indicate that manipulation of CB(2)R may have therapeutic value in MS, but its complexity remains to be considered and studied for further clinical application.

Cannabinoid type 2 receptor activation downregulates stroke-induced classic and alternative brain macrophage/microglial activation concomitant to neuroprotection

BACKGROUND AND PURPOSE

Ischemic stroke continues to be one of the main causes of death worldwide. Inflammation accounts for a large part of damage in this pathology. The cannabinoid type 2 receptor (CB2R) has been proposed to have neuroprotective properties in neurological diseases. Therefore, our aim was to determine the effects of the activation of CB2R on infarct outcome and on ischemia-induced brain expression of classic and alternative markers of macrophage/microglial activation.

METHODS

Swiss wild-type and CB2R knockout male mice were subjected to a permanent middle cerebral artery occlusion. Mice were treated with either a CB2R agonist (JWH-133), with or without a CB2R antagonist (SR144528) or vehicle. Infarct outcome was determined by measuring infarct volume and neurological outcome. An additional group of animals was used to assess mRNA and protein expression of CB2R, interleukin (IL)-1β, IL-6, tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide (MIP) -1α, RANTES, inducible nitric oxide synthase (iNOS), cyclooxygenase-2, IL-4, IL-10, transforming growth factor β (TGF-β), arginase I, and Ym1.

RESULTS

Administration of JWH-133 significantly improved infarct outcome, as shown by a reduction in brain infarction and neurological impairment. This effect was reversed by the CB2R antagonist and was absent in CB2R knockout mice. Concomitantly, administration of JWH-133 led to a lower intensity of Iba1+ microglia/macrophages and a decrease in middle cerebral artery occlusion-induced gene expression of both classic (IL-6, TNF-α, MCP-1, MIP-1α, RANTES, and iNOS) and alternative mediators/markers (IL-10, TGF-β, and Ym1) of microglial/macrophage activation after permanent middle cerebral artery occlusion.

CONCLUSIONS

The inhibitory effect of CB2R on the activation of different subpopulations of microglia/macrophages may account for the protective effect of the selective CB2R agonist JWH-133 after stroke.

Endocannabinoid system and psychiatry: in search of a neurobiological basis for detrimental and potential therapeutic effects

Public concern on mental health has noticeably increased given the high prevalence of neuropsychiatric disorders. Cognition and emotionality are the most affected functions in neuropsychiatric disorders, i.e., anxiety disorders, depression, and schizophrenia. In this review, most relevant literature on the role of the endocannabinoid (eCB) system in neuropsychiatric disorders will be presented. Evidence from clinical and animal studies is provided for the participation of CB1 and CB2 receptors (CB1R and CB2R) in the above mentioned neuropsychiatric disorders. CBRs are crucial in some of the emotional and cognitive impairments reported, although more research is required to understand the specific role of the eCB system in neuropsychiatric disorders. Cannabidiol (CBD), the main non-psychotropic component of the Cannabis sativa plant, has shown therapeutic potential in several neuropsychiatric disorders. Although further studies are needed, recent studies indicate that CBD therapeutic effects may partially depend on facilitation of eCB-mediated neurotransmission. Last but not least, this review includes recent findings on the role of the eCB system in eating disorders. A deregulation of the eCB system has been proposed to be in the bases of several neuropsychiatric disorders, including eating disorders. Cannabis consumption has been related to the appearance of psychotic symptoms and schizophrenia. In contrast, the pharmacological manipulation of this eCB system has been proposed as a potential strategy for the treatment of anxiety disorders, depression, and anorexia nervosa. In conclusion, the eCB system plays a critical role in psychiatry; however, detrimental consequences of manipulating this endogenous system cannot be underestimated over the potential and promising perspectives of its therapeutic manipulation.

The role of central CB2 cannabinoid receptors on food intake in neonatal chicks

The endocannabinoids (ECBs) have diverse physiological functions including the regulation of food intake and metabolism. In mammals, ECBs regulate feeding primarily through the CB1 receptors within the brain whereas the CB2 receptors are primarily involved in the regulation of immune function by direct action on peripheral immune cells and central glia. The central effect of ECBs on feeding behavior has not been studied in non-mammalian species. Therefore, the present study investigated the effect of CB65, a selective CB2 receptors agonist, on food intake in the neonatal chicks. In addition, the effect of astressin, a CRF receptor antagonist, on CB65-induced food intake was also investigated. Intracerebroventricular injection of the CB65 (1.25 μg) increased the food intake at 30- and 60-min post-injection significantly as compared to the control group. Pretreatment with a selective CB2 receptor antagonist, AM630, but not astressin, significantly attenuated the CB65-induced food intake. These results suggested that CB2 receptor agonists act on the brain to induce food intake.

Phytocannabinoids as novel therapeutic agents in CNS disorders

The Cannabis sativa herb contains over 100 phytocannabinoid (pCB) compounds and has been used for thousands of years for both recreational and medicinal purposes. In the past two decades, characterisation of the body's endogenous cannabinoid (CB) (endocannabinoid, eCB) system (ECS) has highlighted activation of central CB(1) receptors by the major pCB, Δ(9)-tetrahydrocannabinol (Δ(9)-THC) as the primary mediator of the psychoactive, hyperphagic and some of the potentially therapeutic properties of ingested cannabis. Whilst Δ(9)-THC is the most prevalent and widely studied pCB, it is also the predominant psychotropic component of cannabis, a property that likely limits its widespread therapeutic use as an isolated agent. In this regard, research focus has recently widened to include other pCBs including cannabidiol (CBD), cannabigerol (CBG), Δ(9)tetrahydrocannabivarin (Δ(9)-THCV) and cannabidivarin (CBDV), some of which show potential as therapeutic agents in preclinical models of CNS disease. Moreover, it is becoming evident that these non-Δ(9)-THC pCBs act at a wide range of pharmacological targets, not solely limited to CB receptors. Disorders that could be targeted include epilepsy, neurodegenerative diseases, affective disorders and the central modulation of feeding behaviour. Here, we review pCB effects in preclinical models of CNS disease and, where available, clinical trial data that support therapeutic effects. Such developments may soon yield the first non-Δ(9)-THC pCB-based medicines.

Cloning and pharmacological characterization of the dog cannabinoid CB₂receptor

Comparison of human, rat and mouse cannabinoid CB(2) receptor primary sequences has shown significant divergence at the mRNA and protein sequence level, raising the possibility of species specific pharmacological properties. Additionally, given the importance of the dog as a non-rodent species for predicting human safety during the drug development process, we cloned the dog CB(2) receptor gene and characterized its in-vitro pharmacological properties in a recombinant expression system. A 1.1 kb dog peripheral cannabinoid receptor (dCB(2)) fragment encoding a 360 amino acid protein was cloned from dog spleen cDNA. Analysis of the cloned dCB(2) polypeptide sequence revealed that it shares between 76 and 82% homology with rat, mouse, human and predicted chimpanzee cannabinoid CB(2) receptors. The dog CB(2) receptor expressed in CHO cells displayed similar binding affinities for various synthetic and endogenous cannabinoids as compared to those measured for the human and rat cannabinoid CB(2) receptors. However, these ligands exhibited altered functional potencies and efficacies for the dog cannabinoid CB(2) receptor, which was also found to be negatively coupled to adenylate cyclase activity. These complex pharmacological differences observed across species for the cannabinoid CB(2) receptor suggest that caution should be exerted when analyzing the outcome of animal efficacy and safety studies, notably those involving cannabinoid CB(2) receptor targeting molecules tested in the dog.

Immunomodulatory properties of kappa opioids and synthetic cannabinoids in HIV-1 neuropathogenesis

Anti-retroviral therapy (ART) has had a tremendous impact on the clinical outcomes of HIV-1 infected individuals. While ART has produced many tangible benefits, chronic, long-term consequences of HIV infection have grown in importance. HIV-1-associated neurocognitive disorder (HAND) represents a collection of neurological syndromes that have a wide range of functional cognitive impairments. HAND remains a serious threat to AIDS patients, and there currently remains no specific therapy for the neurological manifestations of HIV-1. Based upon work in other models of neuroinflammation, kappa opioid receptors (KOR) and synthetic cannabinoids have emerged as having neuroprotective properties and the ability to dampen pro-inflammatory responses of glial cells; properties that may have a positive influence in HIV-1 neuropathogenesis. The ability of KOR ligands to inhibit HIV-1 production in human microglial cells and CD4 T lymphocytes, demonstrate neuroprotection, and dampen chemokine production in astrocytes provides encouraging data to suggest that KOR ligands may emerge as potential therapeutic agents in HIV neuropathogenesis. Based upon findings that synthetic cannabinoids inhibit HIV-1 expression in human microglia and suppress production of inflammatory mediators such as nitric oxide (NO) in human astrocytes, as well as a substantial literature demonstrating neuroprotective properties of cannabinoids in other systems, synthetic cannabinoids have also emerged as potential therapeutic agents in HIV neuropathogenesis. This review focuses on these two classes of compounds and describes the immunomodulatory and neuroprotective properties attributed to each in the context of HIV neuropathogenesis.

Cannabinoid neuroimmune modulation of SIV disease

Marijuana is one of the most commonly used and abused drugs. Δ-9-tetrahydrocannabinol (Δ-9-THC), the primary psychoactive component in marijuana, is FDA-approved to ameliorate AIDS-associated wasting. Because cannabinoid receptors are expressed on cells of the immune system, it is possible that chronic Δ-9-THC use may impact HIV disease progression. Until recently, longitudinal, controlled, systems-approach studies on the effects of cannabinoids on disease progression were lacking. Data from our controlled studies in non-human primates show chronic Δ-9-THC administration prior to and during simian immunodeficiency virus (SIV) infection ameliorates disease progression, attenuates viral load and tissue inflammation, significantly reducing morbidity and mortality of SIV-infected macaques. Identification of possible mechanisms responsible for this modulation of disease progression is complicated due to the multiplicity of cannabinoid-mediated effects, tissue-specific responses to the viral infection, multiple cellular mechanisms involved in inflammatory responses, coordinated neuroendocrine and localized responses to infection, and kinetics of viral replication. Emerging results from our studies reveal that the overall mechanisms mediating the protective effects of cannabinoids involve novel epigenomic regulatory mechanisms in need of systematic investigation. Here, we review the evidence supporting an immunomodulatory role for cannabinoids and its impact on disease progression with focus on HIV/SIV infection.

Cannabinoids as novel anti-inflammatory drugs

Cannabinoids are a group of compounds that mediate their effects through cannabinoid receptors. The discovery of Δ9-tetrahydrocannabinol (THC) as the major psychoactive principle in marijuana, as well as the identification of cannabinoid receptors and their endogenous ligands, has led to a significant growth in research aimed at understanding the physiological functions of cannabinoids. Cannabinoid receptors include CB1, which is predominantly expressed in the brain, and CB2, which is primarily found on the cells of the immune system. The fact that both CB1 and CB2 receptors have been found on immune cells suggests that cannabinoids play an important role in the regulation of the immune system. Recent studies demonstrated that administration of THC into mice triggered marked apoptosis in T cells and dendritic cells, resulting in immunosuppression. In addition, several studies showed that cannabinoids downregulate cytokine and chemokine production and, in some models, upregulate T-regulatory cells (Tregs) as a mechanism to suppress inflammatory responses. The endocannabinoid system is also involved in immunoregulation. For example, administration of endocannabinoids or use of inhibitors of enzymes that break down the endocannabinoids, led to immunosuppression and recovery from immune-mediated injury to organs such as the liver. Manipulation of endocannabinoids and/or use of exogenous cannabinoids in vivo can constitute a potent treatment modality against inflammatory disorders. This review will focus on the potential use of cannabinoids as a new class of anti-inflammatory agents against a number of inflammatory and autoimmune diseases that are primarily triggered by activated T cells or other cellular immune components.

Cannabinoids inhibit migration of microglial-like cells to the HIV protein Tat

Microglia are a population of macrophage-like cells in the central nervous system (CNS) which, upon infection by the human immunodeficiency virus (HIV), secrete a plethora of inflammatory factors, including the virus-specified trans-activating protein Tat. Tat has been implicated in HIV neuropathogenesis since it elicits chemokines, cytokines, and a chemotactic response from microglia. It also harbors a β-chemokine receptor binding motif, articulating a mode by which it acts as a migration stimulus. Since select cannabinoids have anti-inflammatory properties, cross the blood-brain barrier, and target specific receptors, they have potential to serve as agents for dampening untoward neuroimmune responses. The aim of this study was to investigate the effect of select cannabinoids on the migration of microglial-like cells toward Tat. Using a mouse BV-2 microglial-like cell model, it was demonstrated that the exogenous cannabinoids Delta-9-tetrahydrocannabinol (THC) and CP55940 exerted a concentration-related reduction in the migration of BV-2 cells towards Tat. A similar inhibitory response was obtained when the endogenous cannabinoid 2-arachidonoylglycerol (2-AG) was used. The CB(2) receptor (CB2R) antagonist SR144528, but not the CB(1) receptor (CB1R) antagonist SR141716A, blocked this inhibition of migration. Similarly, CB2R knockdown with small interfering RNA reversed the cannabinoid-mediated inhibition. In addition, the level of the β-chemokine receptor CCR-3 was reduced and its intracellular compartmentation was altered. These results indicate that cannabinoid-mediated inhibition of BV-2 microglial-like cell migration to Tat is linked functionally to the CB2R. Furthermore, the results indicate that activation of the CB2R leads to altered expression and compartmentation of the β-chemokine receptor CCR-3.

Cannabinoid receptor agonist protects cultured dopaminergic neurons from the death by the proteasomal dysfunction

Cannabinoids have been proposed to possess neuroprotective properties; though their mechanism of action remains contentious, they are posited to prevent neurodegenerative disorders, including Parkinson's disease, the pathogenesis of which has not been established. Recent studies have demonstrated that induction of proteasomal dysfunction in animal models results in a phenotype similar to Parkinson's disease. Here, we investigated the neuroprotective function of a synthetic cannabinoid-receptor agonist (WIN55.212.2) in dopaminergic neuronal death induced by a proteasomal synthase inhibitor (PSI), additionally testing the hypothesis that WIN55.212.2 modulates cytoplasmic accumulation of parkin and α-synuclein, a key feature of proteasomal dysfunction in Parkinson's. WIN55.212.2 protects PC12 cells from PSI-induced cytotoxicity, concomitantly inhibiting PSI-induced polyADP ribose polymerase expression and activation of caspase-3. While PSI induces cytoplasmic accumulation of α-synuclein and parkin, WIN55.212.2 counters these effects. Interestingly, however, while PSI induces the activation and nuclear translocalization of nuclear factor κB, WIN55.212.2 potentiates this effect. These data are suggestive that WIN55.212.2 might confer a neuroprotective benefit in PSI-induced proteasomal dysfunction, and could further protect against neuronal degeneration stemming from cytoplasmic accumulation of α-synuclein and parkin. These results indicate that WIN55.212.2 may be a candidate for treatment of neurodegenerative diseases, including Parkinson's disease.

Physiology of microglia

Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

HIV-1 infection and alcohol abuse: neurocognitive impairment, mechanisms of neurodegeneration and therapeutic interventions

Clinical studies indicate that alcohol dependence has an additive effect on cognitive deficits associated with HIV-1 infection. Findings in humans and animal models suggest that alcohol, similar to HIV-1, induces inflammatory processes in the brain leading to neurodegeneration. The causes of HIV-1-associated neurotoxicity are comparable to those mediating alcohol-induced neuronal injury. This review aims to present the mechanisms of the combined effects of HIV-1 and alcohol abuse in the brain and to discuss neuroprotective therapies. Oxidative stress, overproduction of pro-inflammatory factors, impairment of blood-brain barrier and glutamate associated neurotoxicity appear to play important roles in alcohol driven neurodegeneration. Diminution of neuroinflammation constitutes a logical approach for prevention of HIV-1 and alcohol mediated neurodegeneration. Agonists of cannabinoid receptor 2 (CB₂) possess potent anti-inflammatory and neuroprotective properties. We address multifaceted beneficial effects of CB₂ activation in the setting of HIV-1 brain infection and alcohol abuse.

An amyloid β42-dependent deficit in anandamide mobilization is associated with cognitive dysfunction in Alzheimer's disease

The endocannabinoids and their attending cannabinoid (CB)(1) receptors have been implicated in the control of cognition, but their possible roles in dementias are still unclear. In the present study, we used liquid chromatography/mass spectrometry to conduct an endocannabinoid-targeted lipidomic analysis of postmortem brain samples from 38 Alzheimer's disease (AD) patients and 17 control subjects, matched for age and postmortem interval. The analysis revealed that midfrontal and temporal cortex tissue from AD patients contains, relative to control subjects, significantly lower levels of the endocannabinoid anandamide and its precursor 1-stearoyl, 2-docosahexaenoyl-sn-glycero-phosphoethanolamine-N-arachidonoyl (NArPE). No such difference was observed with the endocannabinoid 2-arachidonoyl-sn-glycerol or 15 additional lipid species. In AD patients, but not in control subjects, statistically detectable positive correlations were found between (1) anandamide content in midfrontal cortex and scores of the Kendrick's Digit Copy test (p = 0.004, r = 0.81; n = 10), which measures speed of information processing; and (2) anandamide content in temporal cortex and scores of the Boston Naming test (p = 0.027, r = 0.52; n = 18), which assesses language facility. Furthermore, anandamide and NArPE levels in midfrontal cortex of the study subjects inversely correlated with levels of the neurotoxic amyloid peptide, amyloid β-protein (Aβ)(42), while showing no association with Aβ(40) levels, amyloid plaque load or tau protein phosphorylation. Finally, high endogenous levels of Aβ(42) in Swedish mutant form of amyloid precursor protein (APP(SWE))/Neuro-2a cells directly reduced anandamide and NArPE concentrations in cells lysates. The results suggest that an Aβ(42)-dependent impairment in brain anandamide mobilization contributes to cognitive dysfunction in AD.

Overexpression of CB2 cannabinoid receptors results in neuroprotection against behavioral and neurochemical alterations induced by intracaudate administration of 6-hydroxydopamine

The role of CB2 cannabinoid receptors in the behavioral and neurochemical changes induced by intracaudate administration of 6-hydroxydopamine (6-OHDA) was evaluated. 6-OHDA (12 μg/4 μL) or its vehicle was injected in the caudate-putamen (CPu) of mice overexpressing the CB2 cannabinoid receptor (CB2xP) and wild type (WT) mice. Motor impairment, emotional behavior, and cognitive alterations were evaluated. Tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were measured by immunocytochemistry in the CPu and/or substantia nigra (SN) of CB2xP mice and WT mice. Oxidative/nitrosative and neuroinflammatory parameters were also measured in the CPu and cortex of 6-OHDA-treated and sham-treated mice. 6-OHDA-treated CB2xP mice presented significantly less motor deterioration than 6-OHDA-treated WT mice. Immunocytochemical analysis of tyrosine hydroxylase in the SN and CPu revealed significantly fewer lesions in CB2xP mice than in WT mice. GFAP and Iba-1 immunostaining revealed less astrocyte and microglia recruitment to the treated area of the CPu in CB2xP mice. Malonyldialdehyde (MDA) concentrations were lower in the striatum and cerebral cortex of sham-treated CB2xP mice than in sham-treated WT mice. The administration of 6-OHDA increased MDA levels in both WT mice and CB2xP mice; it increased the oxidized (GSSG)/reduced (GSH) glutathione ratio in the striatum in WT mice alone compared with matched sham-treated controls. The results revealed that overexpression of CB2 cannabinoid receptors decreased the extent of motor impairment and dopaminergic neuronal loss, reduced the recruitment of astrocytes and microglia to the lesion, and decreased the level of various oxidative parameters. These results suggest that CB2 receptors offer neuroprotection against dopaminergic injury.

The endocannabinoid system as a target for the treatment of neurodegenerative disease

The Cannabis sativa plant has been exploited for medicinal, agricultural and spiritual purposes in diverse cultures over thousands of years. Cannabis has been used recreationally for its psychotropic properties, while effects such as stimulation of appetite, analgesia and anti-emesis have lead to the medicinal application of cannabis. Indeed, reports of medicinal efficacy of cannabis can been traced back as far as 2700 BC, and even at that time reports also suggested a neuroprotective effect of the cultivar. The discovery of the psychoactive component of cannabis resin, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) occurred long before the serendipitous identification of a G-protein coupled receptor at which Delta(9)-THC is active in the brain. The subsequent finding of endogenous cannabinoid compounds, the synthesis of which is directed by neuronal excitability and which in turn served to regulate that excitability, further widened the range of potential drug targets through which the endocannabinoid system can be manipulated. As a result of this, alterations in the endocannabinoid system have been extensively investigated in a range of neurodegenerative disorders. In this review we examine the evidence implicating the endocannabinoid system in the cause, symptomatology or treatment of neurodegenerative disease. We examine data from human patients and compare and contrast this with evidence from animal models of these diseases. On the basis of this evidence we discuss the likely efficacy of endocannabinoid-based therapies in each disease context.

Endocannabinoids prevent β-amyloid-mediated lysosomal destabilization in cultured neurons

Neuronal cell loss underlies the pathological decline in cognition and memory associated with Alzheimer disease (AD). Recently, targeting the endocannabinoid system in AD has emerged as a promising new approach to treatment. Studies have identified neuroprotective roles for endocannabinoids against key pathological events in the AD brain, including cell death by apoptosis. Elucidation of the apoptotic pathway evoked by β-amyloid (Aβ) is thus important for the development of therapeutic strategies that can thwart Aβ toxicity and preserve cell viability. We have previously reported that lysosomal membrane permeabilization plays a distinct role in the apoptotic pathway initiated by Aβ. In the present study, we provide evidence that the endocannabinoid system can stabilize lysosomes against Aβ-induced permeabilization and in turn sustain cell survival. We report that endocannabinoids stabilize lysosomes by preventing the Aβ-induced up-regulation of the tumor suppressor protein, p53, and its interaction with the lysosomal membrane. We also provide evidence that intracellular cannabinoid type 1 receptors play a role in stabilizing lysosomes against Aβ toxicity and thus highlight the functionality of these receptors. Given the deleterious effect of lysosomal membrane permeabilization on cell viability, stabilization of lysosomes with endocannabinoids may represent a novel mechanism by which these lipid modulators confer neuroprotection.

Neuroimmune pharmacology from a neuroscience perspective

The focus of this commentary is to describe how neuroscience, immunology, and pharmacology intersect and how interdisciplinary research involving these areas has expanded knowledge in the area of neuroscience, in particular. Examples are presented to illustrate that the brain can react to the peripheral immune system and possesses immune function and that resident immune molecules play a role in normal brain physiology. In addition, evidence is presented that the brain immune system plays an important role in mediating neurodegenerative diseases, the aging process, and neurodevelopment and synaptic plasticity. The identification of these mechanisms has been facilitated by pharmacological studies and has opened new possibilities for pharmacotherapeutic approaches to the treatment of brain disorders. The emerging field of neuroimmune pharmacology exemplifies this interdisciplinary approach and has facilitated the study of basic cellular and molecular events and disease states and opens avenues for novel therapies.

Cannabinoids and Dementia: A Review of Clinical and Preclinical Data

The endocannabinoid system has been shown to be associated with neurodegenerative diseases and dementia. We review the preclinical and clinical data on cannabinoids and four neurodegenerative diseases: Alzheimer’s disease (AD), Huntington’s disease (HD), Parkinson’s disease (PD) and vascular dementia (VD). Numerous studies have demonstrated an involvement of the cannabinoid system in neurotransmission, neuropathology and neurobiology of dementias. In addition, several candidate compounds have demonstrated efficacy in vitro. However, some of the substances produced inconclusive results in vivo. Therefore, only few trials have aimed to replicate the effects seen in animal studies in patients. Indeed, the literature on cannabinoid administration in patients is scarce. While preclinical findings suggest causal treatment strategies involving cannabinoids, clinical trials have only assessed the suitability of cannabinoid receptor agonists, antagonists and cannabidiol for the symptomatic treatment of dementia. Further research is needed, including in vivo models of dementia and human studies.

Brain CB₂ Receptors: Implications for Neuropsychiatric Disorders

Although previously thought of as the peripheral cannabinoid receptor, it is now accepted that the CB₂ receptor is expressed in the central nervous system on microglia, astrocytes and subpopulations of neurons. Expression of the CB₂ receptor in the brain is significantly lower than that of the CB₁ receptor. Conflicting findings have been reported on the neurological effects of pharmacological agents targeting the CB₂ receptor under normal conditions. Under inflammatory conditions, CB₂ receptor expression in the brain is enhanced and CB₂ receptor agonists exhibit potent anti-inflammatory effects. These findings have prompted research into the CB₂ receptor as a possible target for the treatment of neuroinflammatory and neurodegenerative disorders. Neuroinflammatory alterations are also associated with neuropsychiatric disorders and polymorphisms in the CB₂ gene have been reported in depression, eating disorders and schizophrenia. This review will examine the evidence to date for a role of brain CB₂ receptors in neuropsychiatric disorders.

Immunoregulation of a CB2 receptor agonist in a murine model of neuroAIDS

Chronic HIV-1 infection commonly affects behavioral, cognitive, and motor functions in the infected human host and is commonly referred to as HIV-1-associated neurocognitive disorders (HAND). This occurs, in measure, as a consequence of ingress of leukocytes into brain perivascular regions. Such cells facilitate viral infection and disease by eliciting blood-brain barrier and neuronal network dysfunctions. Previous works demonstrated that the endocannabinoid system modulates neuroimmunity and as such neuronal and glial functions. Herein, we investigated CB2R receptor expression in murine HIV-1 encephalitis (HIVE) and the abilities of a highly selective CB2R agonist, Gp1a, to modulate disease. HIV-1-infected human monocyte-derived macrophages were injected into the caudate and putamen of immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL/HIVE). Brains of hu-PBL/HIVE mice showed microglial activation and increased expression of CB2R, but not CB1R or GPR55. Gp1a substantively reduced infiltration of human cells into the mouse brain and reduced HLA DQ activation. Gp1a down modulated CCR5 expression on human cells in the spleen with an increase in Fas ligand expression. Our results support the notion that CB2 receptor agonists may be a viable therapeutic candidate for HAND.

The cannabinoid CB2 receptor as a target for inflammation-dependent neurodegeneration

Endocannabinoids are released following brain injury and may protect against excitotoxic damage during the acute stage of injury. Brain injury also activates microglia in a secondary inflammatory phase of more widespread damage. Most drugs targeting the acute stage are not effective if administered more than 6 hours after injury. Therefore, drugs targeting microglia later in the neurodegenerative cascade are desirable. We have found that cannabinoid CB2 receptors are up-regulated during the activation of microglia following brain injury. Specifically, CB2-positive cells appear in the rat brain following both hypoxia-ischemia (HI) and middle cerebral artery occlusion (MCAO). This may regulate post-injury microglial activation and inflammatory functions. In this paper we review in vivo and in vitro studies of CB2 receptors in microglia, including our results on CB2 expression post-injury. Taken together, studies show that CB2 is up-regulated during a process in which microglia become primed to proliferate, and then become fully reactive. In addition, CB2 activation appears to prevent or decrease microglial activation. In a rodent model of Alzheimer's disease microglial activation was completely prevented by administration of a selective CB2 agonist. The presence of CB2 receptors in microglia in the human Alzheimer's diseased brain suggests that CB2 may provide a novel target for a range of neuropathologies. We conclude that the administration of CB2 agonists and antagonists may differentially alter microglia-dependent neuroinflammation. CB2 specific compounds have considerable therapeutic appeal over CB1 compounds, as the exclusive expression of CB2 on immune cells within the brain provides a highly specialised target, without the psychoactivity that plagues CB1 directed therapies.

R-flurbiprofen reduces neuropathic pain in rodents by restoring endogenous cannabinoids

Background

R-flurbiprofen, one of the enantiomers of flurbiprofen racemate, is inactive with respect to cyclooxygenase inhibition, but shows analgesic properties without relevant toxicity. Its mode of action is still unclear.

Methodology/Principal Findings

We show that R-flurbiprofen reduces glutamate release in the dorsal horn of the spinal cord evoked by sciatic nerve injury and thereby alleviates pain in sciatic nerve injury models of neuropathic pain in rats and mice. This is mediated by restoring the balance of endocannabinoids (eCB), which is disturbed following peripheral nerve injury in the DRGs, spinal cord and forebrain. The imbalance results from transcriptional adaptations of fatty acid amide hydrolase (FAAH) and NAPE-phospholipase D, i.e. the major enzymes involved in anandamide metabolism and synthesis, respectively. R-flurbiprofen inhibits FAAH activity and normalizes NAPE-PLD expression. As a consequence, R-Flurbiprofen improves endogenous cannabinoid mediated effects, indicated by the reduction of glutamate release, increased activity of the anti-inflammatory transcription factor PPARγ and attenuation of microglia activation. Antinociceptive effects are lost by combined inhibition of CB1 and CB2 receptors and partially abolished in CB1 receptor deficient mice. R-flurbiprofen does however not cause changes of core body temperature which is a typical indicator of central effects of cannabinoid-1 receptor agonists.

Conclusion

Our results suggest that R-flurbiprofen improves the endogenous mechanisms to regain stability after axonal injury and to fend off chronic neuropathic pain by modulating the endocannabinoid system and thus constitutes an attractive, novel therapeutic agent in the treatment of chronic, intractable pain.

The endocannabinoid system and amyloid-related diseases

The endocannabinoid system may be the target of novel therapies in a wide variety of diseases. Among them, those related with amyloid accumulation will be discussed in the present review. Several components of this system (CB1 and CB2 receptors, endocannabinoids, FAAH enzyme) may participate in different aspects of amyloid pathophysiology such as, for instance, synaptic activity, cell migration, cytokine production or phagocytic activity. Consistent with recent data, putative lines of research and hypothesis will be discussed.

Evidence that MDMA ('ecstasy') increases cannabinoid CB2 receptor expression in microglial cells: role in the neuroinflammatory response in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') produces selective long-lasting serotonergic neurotoxicity in rats. The drug also produces acute hyperthermia which modulates the severity of the neurotoxic response. In addition, MDMA produces signs of neuroinflammation reflected as microglial activation and an increase in the release of interleukin-1beta, the latter of which appears to be a consequence of the hyperthermic response and to be implicated in the neurotoxicity induced by the drug. Over-expression of the cannabinoid CB2 receptor in microglia during non-immune and immune pathological conditions is thought to be aimed at controlling the production of neurotoxic factors such as proinflammatory cytokines. Our objective was to study the pattern of CB2 receptor expression following MDMA and to examine the effect of JWH-015 (a CB2 agonist) on the MDMA-induced neuroinflammatory response as well as 5-hydroxytryptamine (5-HT) neurotoxicity. Adult Dark Agouti rats were given MDMA (12.5 mg/kg, i.p.) and killed 3 h or 24 h later for the determination of CB2 receptor expression. JWH-015 was given 48 h, 24 h and 0.5 h before MDMA and 1 h and/or 6 h later and animals were killed for the determination of microglial activation (3 h and 24 h) and 5-HT neurotoxicity (7 days). MDMA increased CB2 receptor expression shortly after administration and these receptors were found in microglia. JWH-015 decreased MDMA-induced microglial activation and interleukin-1beta release and slightly decreased MDMA-induced 5-HT neurotoxicity. In conclusion, CB2 receptor activation reduces the neuroinflammatory response following MDMA and provides partial neuroprotection against the drug.

2,3-Dihydro-1-benzofuran derivatives as a series of potent selective cannabinoid receptor 2 agonists: design, synthesis, and binding mode prediction through ligand-steered modeling

We recently discovered and reported a series of N-alkyl-isatin acylhydrazone derivatives that are potent cannabinoid receptor 2 (CB(2)) agonists. In an effort to improve the druglike properties of these compounds and to better understand and improve the treatment of neuropathic pain, we designed and synthesized a new series of 2,3-dihydro-1-benzofuran derivatives bearing an asymmetric carbon atom that behave as potent selective CB(2) agonists. We used a multidisciplinary medicinal chemistry approach with binding mode prediction through ligand-steered modeling. Enantiomer separation and configuration assignment were carried out for the racemic mixture for the most selective compound, MDA7 (compound 18). It appeared that the S enantiomer, compound MDA104 (compound 33), was the active enantiomer. Compounds MDA42 (compound 19) and MDA39 (compound 30) were the most potent at CB(2). MDA42 was tested in a model of neuropathic pain and exhibited activity in the same range as that of MDA7. Preliminary ADMET studies for MDA7 were performed and did not reveal any problems.

Cannabinoid activation of peroxisome proliferator-activated receptors: potential for modulation of inflammatory disease

Cannabinoids act via cell surface G protein-coupled receptors (CB(1) and CB(2)) and the ion channel receptor TRPV1. Evidence has now emerged suggesting that an additional target is the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors. There are three PPAR subtypes alpha, delta (also known as beta) and gamma, which regulate cell differentiation, metabolism and immune function. The major endocannabinoids, anandamide and 2-arachidonoylglycerol, and ajulemic acid, a structural analogue of the phytocannabinoid Delta(9)-tetrahydrocannabinol (THC), have anti-inflammatory properties mediated by PPARgamma. Other cannabinoids which activate PPARgamma include N-arachidonoyl-dopamine, THC, cannabidiol, HU210, WIN55212-2 and CP55940. The endogenous acylethanolamines, oleoylethanolamide and palmitoylethanolamide regulate feeding and body weight, stimulate fat utilization and have neuroprotective effects mediated through PPARalpha. Other endocannabinoids that activate PPARalpha include anandamide, virodhamine and noladin ether. There is, as yet, little direct evidence for interactions of cannabinoids with PPARdelta. There is a convergence of effects of cannabinoids, acting via cell surface and nuclear receptors, on immune cell function which provides promise for the targeted therapy of a variety of immune, particularly neuroinflammatory, diseases.

Cannabinoid CB2 receptor agonists protect the striatum against malonate toxicity: relevance for Huntington's disease

Cannabinoid agonists might serve as neuroprotective agents in neurodegenerative disorders. Here, we examined this hypothesis in a rat model of Huntington's disease (HD) generated by intrastriatal injection of the mitochondrial complex II inhibitor malonate. Our results showed that only compounds able to activate CB2 receptors were capable of protecting striatal projection neurons from malonate-induced death. That CB2 receptor agonists are neuroprotective was confirmed by using the selective CB2 receptor antagonist, SR144528, and by the observation that mice deficient in CB2 receptor were more sensitive to malonate than wild-type animals. CB2 receptors are scarce in the striatum in healthy conditions, but they are markedly upregulated after the lesion with malonate. Studies of double immunostaining revealed a significant presence of CB2 receptors in cells labeled with the marker of reactive microglia OX-42, and also in cells labeled with GFAP (a marker of astrocytes). We further showed that the activation of CB2 receptors significantly reduced the levels of tumor necrosis factor-alpha (TNF-alpha) that had been increased by the lesion with malonate. In summary, our results demonstrate that stimulation of CB2 receptors protect the striatum against malonate toxicity, likely through a mechanism involving glial cells, in particular reactive microglial cells in which CB2 receptors would be upregulated in response to the lesion. Activation of these receptors would reduce the generation of proinflammatory molecules like TNF-alpha. Altogether, our results support the hypothesis that CB2 receptors could constitute a therapeutic target to slowdown neurodegeneration in HD.

The activation of cannabinoid CB2 receptors stimulates in situ and in vitro beta-amyloid removal by human macrophages

The endocannabinoid system is a promising therapeutic target in a wide variety of diseases. However, the non-desirable psychotropic effects of natural and synthetic cannabinoids have largely counteracted their clinical usefulness. These effects are mostly mediated by cannabinoid receptors of the CB(1) type, that exhibit a wide distribution in neuronal elements of the CNS. Thus, the presence of other elements of this system in the CNS, such as CB(2) receptors, may open new possibilities for the development of cannabinoid-based therapies. These receptors are almost absent from the CNS in normal conditions but are up-regulated in glial cells under chronic neuroinflammatory stimuli, as has been described in Alzheimer's disease. To understand the functional role of these receptors, we tested their role in the process of beta-amyloid removal, that is currently considered as one of the most promising experimental approaches for the treatment of this disease. Our results show that a CB(2) agonist (JWH-015) is capable of inducing the removal of native beta-amyloid removal from human frozen tissue sections as well as of synthetic pathogenic peptide by a human macrophage cell line (THP-1). Remarkably, this effect was achieved at low doses (maximum effect at 10 nM) and was specific for this type of cells, as U373MG astrocytoma cells did not respond to the treatment. The effect was CB(2)-mediated, at least partially, as the selective CB(2) antagonist SR144528 prevented the JWH-015-induced plaque removal in situ. These data corroborate the possible therapeutic interest of CB(2) cannabinoid specific chemicals in the treatment of Alzheimer's disease.

Cannabinoid receptor type 2 activation induces a microglial anti-inflammatory phenotype and reduces migration via MKP induction and ERK dephosphorylation

Background

Cannabinoid receptor type 2 (CBR2) inhibits microglial reactivity through a molecular mechanism yet to be elucidated. We hypothesized that CBR2 activation induces an anti-inflammatory phenotype in microglia by inhibiting extracellular signal-regulated kinase (ERK) pathway, via mitogen-activated protein kinase-phosphatase (MKP) induction. MKPs regulate mitogen activated protein kinases, but their role in the modulation of microglial phenotype is not fully understood.

Results

JWH015 (a CBR2 agonist) increased MKP-1 and MKP-3 expression, which in turn reduced p-ERK1/2 in LPS-stimulated primary microglia. These effects resulted in a significant reduction of tumor necrosis factor-α (TNF) expression and microglial migration. We confirmed the causative link of these findings by using MKP inhibitors. We found that the selective inhibition of MKP-1 by Ro-31-8220 and PSI2106, did not affect p-ERK expression in LPS+JWH015-treated microglia. However, the inhibition of both MKP-1 and MKP-3 by triptolide induced an increase in p-ERK expression and in microglial migration using LPS+JWH015-treated microglia.

Conclusion

Our results uncover a cellular microglial pathway triggered by CBR2 activation. These data suggest that the reduction of pro-inflammatory factors and microglial migration via MKP-3 induction is part of the mechanism of action of CBR2 agonists. These findings may have clinical implications for further drug development.

Cannabinoids for the treatment of dementia

BACKGROUND

Following the discovery of an endogenous cannabinoid system and the identification of specific cannabinoid receptors in the central nervous system, much work has been done to investigate the main effects of these compounds. There is increasing evidence that the cannabinoid system may regulate neurodegenerative processes such as excessive glutamate production, oxidative stress and neuroinflammation. Neurodegeneration is a feature common to the various types of dementia and this has led to interest in whether cannabinoids may be clinically useful in the treatment of people with dementia. Recent studies have also shown that cannabinoids may have more specific effects in interrupting the pathological process in Alzheimer's disease.

OBJECTIVES

To determine from available research whether cannabinoids are clinically effective in the treatment of dementia.

SEARCH STRATEGY

The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group (CDCIG), The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL and LILACS were searched on 11 April 2008 using the terms: cannabis or cannabinoid* or endocannabinoid* or cannabidiol or THC or CBD or dronabinol or delta-9-tetrahydrocannabinol or marijuana or marihuana or hashish. The CDCIG Specialized Register contains records from all major health care databases (The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS) as well as from many clinical trials registries and grey literature sources.

SELECTION CRITERIA

All double-blind and single (rater)-blind randomized placebo controlled trials assessing the efficacy of cannabinoids at any dose in the treatment of people with dementia.

DATA COLLECTION AND ANALYSIS

Two reviewers independently examined the retrieved studies for inclusion according to the selection criteria. They then independently assessed the methodological quality of selected trials and extracted data where possible.

MAIN RESULTS

Only one study met the inclusion criteria. The data in the study report were presented in such a way that they could not be extracted for further analysis and there was insufficient quantitative data to validate the results.

AUTHORS' CONCLUSIONS

This review finds no evidence that cannabinoids are effective in the improvement of disturbed behaviour in dementia or in the treatment of other symptoms of dementia. More randomized double-blind placebo controlled trials are needed to determine whether cannabinoids are clinically effective in the treatment of dementia.

The endocannabinoid system in neuropathological states

The endocannabinoid system (ECS) exerts important modulatory functions in the central nervous system (CNS), particularly the retrograde control of excitatory or inhibitory synapses, which enables this system to participate in the control of important neurobiological processes in healthy conditions. However, this physiological relevance acquires a maximal interest in neuropathological conditions affecting either the function or the structures of specific areas of the brain, conditions that have been associated with important changes in the activity of this modulatory system (e.g. losses of CB1 receptors (CB1R), up-regulation of CB2 receptors (CB2R), generation of endocannabinoids) that are susceptible to pharmacological adaptation. Among the group of brain disorders that have been associated with the endocannabinoid system, a special interest has been concentrated in various neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and ischemia. These three disorders will be reviewed here from the perspective of the types of changes experienced by the cannabinoid signalling in humans and cellular or animal models, and from a possible usefulness of certain cannabinoid compounds to alleviate symptoms and/or to delay their progression.

Pharmacotherapeutic modulation of the endocannabinoid signalling system in psychiatric disorders: drug-discovery strategies

Medicinal chemistry has produced small-molecule agents with drug-like character that potently and safely modulate the activity of discrete endocannabinoid system components as potential treatments for medical disorders, including various psychiatric conditions. Two cannabinoid (CB) receptors (CB1 and CB2) currently represent prime endocannabinoid-system therapeutic targets for ligands that either mimic endocannabinoid signalling processes and/or potentiate endocannabinoid-system activity (agonists) or attenuate pathologically heightened endocannabinoid-system transmission (antagonists). Two endocannabinoid deactivating enzymes, fatty acid amide hydrolase (FAAH) and soluble monoacylglycerol lipase (MGL), are increasingly prominent targets for inhibitors that indirectly potentiate endocannabinoid-system signalling. Continued profiling of drug candidates in relevant disease models, identification of additional cannabinoid-related therapeutic targets, and validation of new pharmacological modes of endocannabinoid system modulation will undoubtedly invite further translational efforts in the cannabinoid field for treating psychiatric disorders and other medical conditions.

High concentrations of cannabinoids activate apoptosis in human U373MG glioma cells

Cannabinoids bind to two G-protein-coupled receptors, CB1 and CB2, expressed by neurons and cells of the immune system, respectively. Glioma cells (astrocyte-derived brain tumor cells) express cannabinoid receptors, and numerous in vitro and in vivo studies performed in rodents have concluded that apoptosis could be induced by cannabinoids in these cells. Whether this also applies to human cells is controversial; we, therefore, assessed the effect of cannabinoids on human glioma cell viability with the human astrocytoma cell line U373MG. We report here that U373MG human glioma cells are sensitive only to high concentrations of cannabinoids (>5 microg/ml for Delta(9)-THC). Similar concentrations of the compounds promoted a rapid activation of extracellular-regulated kinase and c-Jun NH2-terminal kinase, suggesting that cannabinoid receptors are functional in U373MG cells. Nevertheless, these kinases are not involved in cannabinoid-induced cell death in U373MG cells, insofar as blocking their activation with specific inhibitors does not reduce cell death. CB1 is expressed in U373MG cells and is involved in cannabinoid-induced cell death, in that blocking its activation with a specific antagonist (AM251) almost totally prevented cell death following incubation of the cells with Delta(9)-THC. In addition, as already reported, some cannabinoids may have modest proproliferative properties in U373MG cells. Human U373MG glioma cells are sensitive only to very high, pharmacologically irrelevant concentrations of cannabinoids, so it seems unlikely that cannabinoids would constitute promising molecules for treating malignant astrocytoma; they do not induce glioma cell death at doses that could be applied safely to humans.